ATP-driven chromatin remodeling activity and histone acetyltransferases act sequentially during transactivation by RAR/RXR in vitro

Using a "crude" chromatin-based transcription system that mimics transactiv ation by RAR/RXR heterodimers in vivo, we could not demonstrate that chroma tin remodeling was required to relieve nucleosomal repression. Using "purif ied" chromatin templates, we show here that, irrespective of the presence o f histone H1, both ATP-driven chromatin remodeling activities and histone a cetyltransferase (HAT) activities of coactivators recruited by liganded rec eptors are required to achieve transactivation. DNA footprinting, ChIP anal ysis, and order of addition experiments indicate that coactivator HAT activ ities and two ATP-driven remodeling activities are sequentially involved at distinct steps preceding initiation of transcription. Thus, both ATP-drive n chromatin remodeling and HAT activities act in a temporally ordered and i nterdependent manner to alleviate the repressive effects of nucleosomal his tones on transcription by RAR alpha /RXR alpha heterodimers.